1. Field of the Invention
The present invention relates to a laser-broken fuse, more particularly to that used for a semiconductor device.
2. Description of the Related Art
Conventionally, to prepare a laser-broken fuse used in a memory redundancy technique, a filament fuse made of polysilicon, or molybdenum silicide, etc., is formed on a field oxide film as a part of a wiring layer. On this laser-broken fuse, an interlevel insulating film and a protection layer consisting of a CVD silicon oxide film, BPSG film, PSG film, etc., are formed.
A laser-broken fuse having the above-mentioned structure itself generates heat, and breaks when the heat of the fuse itself exceeds a certain point by irradiation of a laser beam thereon.
At present, as the memory devices are developing rapidly in high integration and mass storage, many more layers are formed in multilayered internal wiring layers, especially wiring layers made of aluminum or copper. In a memory device comprising such a multilayered wiring, the thicknesses of the insulating films such as interlevel insulating film, etc., located close to the fuse, are inevitably increased.
The thickness-increased films, namely, thick insulating films, loaded on a fuse serve to suppress the thermal-explosion force, thereby interfering with breaking of the fuse.
In multilayered wiring device, this problem can be solved by thinning that part of the insulating film which is located on the territory of the fuse to an appropriate thickness for breaking the fuse.
However, in reality, it is very difficult to control, by etching, the thickness of the insulating film since accuracy of the etching varies from time to time.
Meanwhile, the technique for breaking a wiring layer, the main component of which is aluminum or copper, by laser, has not yet been completely realized due to the problem of aluminum or copper not absorbing but reflecting the laser beams. For example, if the intensity of the laser beams is greatly increased to overcome the above problem, the intensity may have to be raised high enough to even damage the field oxide film.
To reiterate, with conventional techniques, it has been very difficult to break a semiconductor device including a multilayered wiring since a fuse made of polysilicon, etc., is located deep within the layer of the apparatus. Further, yielding of the products is accordingly low.
In addition, the technique for breaking a fuse, that is a wiring layer, the main component of which is aluminum or copper, by means of laser, has not yet completely realized.